feat(partition): add support to use backup GPT header

Currently we just use primary GPT header which is located in second
entry after MBR header, but if this block is corrupted or CRC
mismatch occurs we could try to use the backup GPT header located at
LBAn and GPT entries following this from LBA-33.

Add suitable warning messages before returning any errors to identify
the cause of issue.

Change-Id: I0018ae9eafbacb683a18784d2c8bd917c70f50e1
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/include/drivers/partition/partition.h b/include/drivers/partition/partition.h
index ab48e12..8e749c9 100644
--- a/include/drivers/partition/partition.h
+++ b/include/drivers/partition/partition.h
@@ -29,6 +29,8 @@
 
 #define LEGACY_PARTITION_BLOCK_SIZE	512
 
+#define LBA(n) ((unsigned long long)(n) * PLAT_PARTITION_BLOCK_SIZE)
+
 typedef struct partition_entry {
 	uint64_t		start;
 	uint64_t		length;